1) Two types of corticotropin releasing factor (CRF)-like immunoreactivity have been identified in the rat brain and biochemically characterized. One type is obtained in the hypothalamus in fundibular system, the other one in the sensory hindbrain area and the spinal cord. CRF receptors have been identified in the spinal trigeminal and superficial spinal cord areas strengthening the latter suggestion of a presence of CRF in extrahypothalamic primary sensory areas. 2) Capsaicin treatment of newborn rats was previously shown to cause selective degeneration of primary sensory neurons and a depletion of substance P, somatostatin, cholecystokinin and vasoactive intestinal polypeptide from central and peripheral sensory nerves. We now add CRF, calcitonin gene related peptide (CGRP) and galanin (GA) to the list of capsaicin sensitive sensory neuropeptides. CGRP has been shown to be a potent vasodilator and thus seems to be of major interest in blood pressure control. 3) Immunohistochemical distribution of CRF, atrial natriuretic factor (ANF), CGRP, GA and melanin concentrating hormone (MCH) has been demonstrated in the rat brain and stereotaxic atlases were prepared. 4) Using radioimmunoassay (RIA) and the micropunch technique quantitative distribution of CRF, ANF, CGRP and MCH-like peptides in about 50 brain nuclei has been determined. 5) Using RIA and high performance liquid chromatography (HPLC) CRF, MCH, CGRP antisera were biochemically characterized. 6) The autoradiographic distribution of CRF and CGRP receptor sites in the rat brain have been demonstrated.